162 EVOLUTION AND ANIMAL LIFE 



formation of species. As to this it may be said that the possible 

 variation within each species is much greater than the range 

 of the individuals which actually survive. The condition of 

 domestication favors the development of extreme variation, be- 

 cause such individuals may be preserved from interbreeding 

 with the mass, and they may survive even if their characters 

 are unfavorable to competition in the struggle for existence. 

 Among plants it is noticed that new soil and new conditions 

 seem to favor large variation in the progeny, although the traits 

 thus produced are not usually hereditary. Cases more or less 

 analogous to those noted by Dr. de Vries are not rare in horti- 

 culture. The cross breeding of variant forms favors the ap- 

 pearance of new forms. Among actual species in a state of 

 nature, there are very few which seem likely to have arisen by a 

 sudden leap or mutation. The past and the future of de Vries' 

 evening primroses are yet to be shown. The species called by 

 de Vries Oenothera lamarckiana is not at present known in its 

 wild state anywhere in North America, the parent region of all 

 the species of evening primroses or Oenothera; so that we have 

 as yet no reason to assume that the various mutants of the 

 evening primrose are really comparable to the wild species of 

 the same group now existing in America. 



While saltation remains as one of the probable sources of 

 specific difference, the actual role of this process in nature is 

 yet to be proved. 



